Apical position locator

ABSTRACT

A method and system are disclosed for detecting an apical position depending on the change in the impedance between a first electrode inserted into the root canal of the tooth of a patient and a second external electrode applied to a body surface of the patient. According to some embodiments, a regulated current such as an alternating current having a substantially constant amplitude is supplied between the two electrodes, and this current serves as a measurement signal. Alternatively or additionally, the frequency of the time varying (e.g. alternating) current is at least 50 KHZ, and/or at most about 300 KHZ. In some embodiments, the presently disclosed device includes a processing unit which determines a capacitance-governed function when the first electrode is in the apical region, and which determined a function at least moderately governed by resistance when the electrode is in the dental neck region. Optionally, the first electrode inserted into the root canal is a dental file or reamer.

FIELD OF THE INVENTION

The present invention relates to dental treatment, and in particular tomethods and apparatus for detecting an apical position in a root canalof a tooth.

BACKGROUND AND RELATED ART

During the course of dental treatment, dental files are inserted intothe root canal to remove nerve and blood vessels. A major concern is tolocate the apical constriction (minor foramen) for determining theworking length and/or the apex (major foramen) to avoid surpassing theapex into the soft tissue.

Towards this end, a probe or electrode is typically inserted into theroot canal, and the location of the apical region of the tooth isdetected by measuring the resistance or the impedance between theinserted electrode and a second external electrode located outside ofthe tooth, usually connected to oral soft tissue. Thus, as the leadingedge of the root canal probe or electrode approaches the apicalposition, the resistance or impedance between the root canal electrodeand the external electrode changes. The resistance or impedance value iscorrelated with the depth of the probe tip in the root canal, allowingthe dental practitioner to detect the apical position of the tooth.Typically, the apex locator instrument includes a display panel, whichindicates the distance between a fixed point on the probe (e.g. theprobe tip) and a fix point in the apical region (e.g. the apex, or alocation of the apical constriction).

To date, apex locator instruments suffer from a number of shortcomings.For example, in many clinical situations, the value displayed by theapex instrument is not stable, making it difficult for the practitionerto determine the distance between the tip of the probe and the apex orapical constriction. Another source of inaccuracy stems from the factthat root canal dimensions and physical properties vary between specificteeth and patients, and thus many devices provide accurate readings forcertain patients and erroneous readings for others.

Another source of inaccuracy stems from the fact that changes in anamplitude of current through biological tissue between the root canaland another location in the body may change the electrical properties ofthis biological tissue, introducing inaccuracies in a computed distancebetween the probe and the apical region.

Thus, there is an ongoing need for improved methods and apparatus fordetermining the position of a probe or electrode inserted within theroot canal of a tooth.

Below is a listing of patents, published patent applications, andnon-patent publications that provide potentially relevant related art.Each patent, published patent application, and non-patent publication isincorporated herein by reference in its entirety.

U.S. Pat. No. 4,272,531; U.S. Pat. No. 3,993,044; U.S. Pat. No.4,447,206; U.S. Pat. No. 4,243,388; U.S. Pat. No. 3,901,216; U.S. Pat.No. 3,753,434; U.S. Pat. No. 5,096,419; U.S. Pat. No. 5,112,224; U.S.Pat. No. 5,211,556; U.S. Pat. No. 5,295,833 and U.S. Pat. No. 6,221,031.

SUMMARY OF THE INVENTION

The aforementioned needs are satisfied by several aspects of the presentinvention.

It is now disclosed for the first time apparatus for detecting an apicalposition depending on the change in the impedance between a firstcurrent supply electrode inserted into the root canal of a tooth of apatient and a second current supply electrode contacting a body surfaceof the patient. The presently disclosed apparatus includes (a) adetection apparatus including a measurement signal generator adapted toproduce a regulated current (e.g. an alternating current) between thefirst and second current supply electrodes, the detection apparatusadapted to sense an impedance parameter between the first and secondelectrodes (for example, by detecting a voltage parameter that is aknown function of the voltage between the first and second currentsupply electrodes), and (b) a processing unit for deriving from thesensed parameter a multiple of a distance between a fixed point on thefirst current supply electrode and the apical position of the tooth.

According to some embodiments, the regulated current has a substantiallyconstant current amplitude, e.g. a current whose amplitude issubstantially independent of a value of the distance between the fixedpoint on the first current supply electrode and the apical position.

According to some embodiments, the regulated current is a time varyingcurrent (e.g. an alternating current). Time varying regulated currentsof any frequency are within the scope of the present invention.According to some embodiments, the current has a frequency of at least50 KHz. In some embodiments, the current is a “medium frequency”current, having a frequency of at least 50 KHz and at most 300 KH, atmost 250 KHZ, or at most 200 KHZ.

It is noted that, according to some embodiments, during the course ofderiving the multiple of the distance, the processing unit determines acapacitance-governed function when the first electrode (e.g. the fixedpoint of the electrode) is in the apical region, and the processing unitdetermines a function at least moderately governed by resistance whenthe first electrode is in a dental neck region.

According to some embodiments, the presently disclosed device furtherincludes a display unit for displaying output received from theprocessing unit.

It is now disclosed for the first time apparatus for detecting an apicalposition depending on the change in the impedance between a firstcurrent supply electrodes inserted into the root canal of a tooth of apatient and a second current supply electrode contacting a body surfaceof the patient. The presently disclosed apparatus includes (a) adetection apparatus including a measurement signal generator adapted toproduce between the first and second current supply electrodes a voltage(e.g. an alternating current voltage) whose amplitude depends on aposition of the first current supply electrode within the root canal ofthe tooth, the detection apparatus adapted to sense a impedanceparameter between the first and second current supply electrodes and/ora parameter related to a voltage between the first and second currentsupply electrodes, and (b) a processing unit for deriving from thesensed parameter a multiple of a distance between a fixed point on thefirst current supply electrode and the apical position of the tooth.

According to some embodiments, a voltage whose amplitude “substantially”depends on a position of the first current supply electrode within theroot canal of the tooth, e.g. whose amplitude changes by at least 10%,or by at least 30% as the position of the first current supply electrodewithin the root canal changes. In one example, the amplitude of thevoltage changes by at least 10%, or by at least 30% when the fixed pointof the first electrode moves between a dental neck region of the rootcanal and an apical region.

It is now disclosed for the first time a device comprising (a) a dentalfile electrode insertable into the root canal of a tooth of a patient,(b) an external electrode adapted to contact a body surface of thepatient, and (c) a detection apparatus including a measurement signalgenerator adapted to produce a regulated current (e.g. an alternatingcurrent) between the dental file and external electrodes, the detectionapparatus adapted to sense an impedance related parameter to generate anoutput signal indicative of a distance between a fixed point on thedental file electrode and the apical position of the tooth.

It is now disclosed for the first time a device comprising (a) a dentalfile electrode insertable into the root canal of a tooth of a patient,(b) an external electrode adapted to contact a body surface of thepatient and (c) a detection apparatus including a measurement signalgenerator adapted to produce between the dental file and externalelectrodes a voltage whose amplitude depends on a position of the dentalfile electrode within the root canal of the tooth (e.g. a voltage of analternating current), the detection apparatus adapted to sense animpedance related parameter between the first and second current supplyelectrodes (for example, by detecting a voltage parameter that is aknown function of the voltage between the first and second currentsupply electrodes) 4 to generate an output signal indicative of adistance between a fixed point on the first electrode and the apicalposition of the tooth.

According to some embodiments, the presently disclosed device furtherincludes (d) a processing unit for deriving from the output signal amultiple of a distance between the fixed point on the first electrodeand the apical position of the tooth.

It is now disclosed for the first time apparatus for detecting an apicalposition depending on the change in the impedance between a firstelectrode inserted into the root canal of a tooth of a patient and asecond electrode contacting a body surface of the patient. The presentlydisclosed apparatus includes (a) a detection apparatus including ameasurement signal generator adapted to produce electrical signals (e.g.electrical signals of an alternating current) having a frequency of atleast 50 KHZ and at most 200 KHZ (or at most 250 KHZ, or at most 250KHZ) between the first and second power supply a measurement signal, thedetection apparatus adapted to sense an impedance related parameter(e.g. an impedance related parameter between the first and secondelectrodes) and (b) a processing unit for deriving from the sensedparameter a multiple of a distance between a fixed point on the firstelectrode and the apical position of the tooth.

It is now disclosed for the first time a device comprising a dental fileelectrode insertable into the root canal of a tooth of a patient, anexternal electrode adapted to contact a body surface of the patient anda detection apparatus including a measurement signal generator adaptedto produce between the dental file and external electrodes electricalsignals having a frequency of at least 50 KHZ and at most 200 KHZ, thedetection apparatus adapted to sense an impedance related parameter(e.g. an impedance related parameter between the dental file andexternal electrodes) to generate an output signal indicative of adistance between a fixed point on the first electrode and the apicalposition of the tooth.

It is now disclosed for the first time a device comprising (a) a dentalfile electrode insertable into the root canal of a tooth, at least aportion of an elongate surface of the dental file electrode beinguninsulated, (b) an external electrode adapted to contact a bodysurface, and (c) a detection apparatus including a measurement signalgenerator adapted to produce between the dental file and externalelectrodes electrical signals having a frequency of at least 50 KHZ, thedetection apparatus adapted to sense an impedance related parameter(e.g. an impedance related parameter between the dental file andexternal electrode) to generate an output signal indicative of adistance between a fixed point on the first electrode and the apicalposition of the tooth.

As used herein, an “elongate surface” of an elongate body is the surfaceperpendicular to the elongate axis substantially not near each end ofthe elongate body. In one embodiment, the distance between points of the“elongate surface” and an end of the elongate body is at least 0.1 timesthe length of the elongate body. In some embodiments, the distancebetween points of the “elongate surface” and an end of the elongate bodyis at least 0.2 times the length of the elongate body.

It is now disclosed for the first time a device comprising (a) a firstelectrode insertable into the root canal of a tooth of a patient, (b) asecond electrode adapted to contact a body surface of the patient and(c) a detection apparatus including a measurement signal generatoradapted to produce between the first and second electrodes electricalsignals having a frequency of at least 50 KHZ, the detection apparatusadapted to sense an impedance related parameter (e.g. an impedancerelated parameter between the first and second electrodes) to generatean output signal indicative of a distance between a fixed point on thefirst electrode and the apical position of the tooth, the measurementsignal generator adapted to supply a maximum of 40 microamperes betweenthe first and second electrodes.

It is now disclosed for the first time apparatus for detecting an apicalposition depending on the change in the impedance between a firstelectrode inserted into the root canal of a tooth of a patient and asecond electrode contacting a body surface of the patient. The presentlydisclosed apparatus comprises (a) a detection apparatus including ameasurement signal generator adapted to produce a measurement signal(e.g. alternating current) between the first and second electrodes, thedetection apparatus adapted to sense an impedance-related parameter(e.g. by sensing a voltage parameter) between the first and secondcurrent supply electrodes, and (b) a processing unit for deriving fromthe sensed parameter a multiple of a distance between a fixed point onthe first electrode and the apical position of the tooth, wherein theprocessing unit determines a capacitance-governed function when thefirst electrode is in the apical region, and the processing unitdetermines a function at least moderately governed by resistance whenthe electrode is in a dental neck region.

It is now disclosed for the first time a method of measuring penetrationin a root canal of a tooth of a patient. The presently disclosed methodincludes (a) inserting a first electrode into the root canal of a tooth,(b) applying a second electrode to a body surface of the patient, (c)supplying a regulated current between the first and second electrodes,and (d) determining (e.g. measuring) an impedance parameter between thefirst and second electrodes, the impedance parameter indicative of adistance between a fixed point on the first electrode and an apicalposition of the tooth.

According to some embodiments, the second electrode is applied to theposition within the oral cavity of the patient.

Alternatively or additionally, the second electrode is applied to theposition outside of the oral cavity of the patient.

According to some embodiments, the first electrode is inserted to aplurality of depths within the root canal, and an amplitude of theregulated current is substantially independent of the distance betweenthe fixed point and the apical position.

It is noted that each “depth” is characterized by a different distancebetween a fixed point on the first electrode (e.g. the electrode beinginserted into the root canal) and the apical position of the tooth.

According to some embodiments, the regulated current is a substantiallylow amplitude regulated current which never exceeds 40 microamperes whenthe first electrode is near an apical region.

According to some embodiments, the regulated current is a time varyingcurrent, and a frequency of the time varying current is at most 250 KHZ,or at most 300 KHZ, or at most 200 KHZ.

According to some embodiments, the regulated current is a time varyingcurrent, and a frequency of the time varying current is at least 25 KHZ,or at least 50 KHZ.

According to some embodiments, the time varying current is has afrequency between 50 KHZ and 200 KHZ, or between 50 KHZ and 250 KHZ, orbetween 50 KHZ and 300 KHZ.

According to some embodiments, the determining includes determining acapacitance-determined impedance parameter when the fixed point is in anapical region of the root canal, and determining an impedance parameterwhose value is at least moderately governed by resistance when the fixedpoint is in a dental neck region of the root canal.

According to some embodiments, the first electrode is a dental file.

According to some embodiments, at least a portion of an elongate surfaceof the first electrode is uninsulated.

According to some embodiments, the presently disclosed method furtherincludes the step of deriving from the determined impedance parameter amultiple of a distance between the fixed point on the electrode and theapical position of the tooth.

According to some embodiments, the deriving includes deriving acapacitance-governed function when the fixed point is in an apicalregion of the root canal, and deriving a function at least moderatelygoverned by resistance when the fixed point is in a dental neck regionof the root canal.

It is now disclosed for the first time a method of measuring penetrationin a root canal of a tooth of a patient. The presently disclosed methodincludes inserting a first electrode into a root canal of a tooth, (b)applying a second electrode to a body surface of the patient, (c)supplying a measurement signal between the first and second electrodesand (d) determining (e.g. measuring) an impedance parameter between thefirst and second electrodes, the impedance parameter indicative of adistance between a fixed point on the first electrode and an apicalposition of the tooth, wherein the first electrode is inserted to aplurality of distinct depths within the root canal, and for each thedepth, an amplitude voltage of the measurement signals depends, orsubstantially depends, on the distance between the fixed point and theapical position.

It is now disclosed for the first time a method of measuring penetrationin a root canal of a tooth of a patient. The presently disclosed methodincludes (a) inserting a first electrode into a root canal of a tooth,(b) applying a second electrode to a body surface of the patient, (c)supplying an electrical measurement signal (e.g. alternating current)having a frequency of at least 50 KHZ between the first and secondelectrodes, and (d) determining (e.g. measuring) an impedance parameterbetween the first and second electrodes, the impedance parameterindicative of a distance between a fixed point on the first electrodeand an apical position of the tooth.

According to some embodiments, at least a portion of an elongate surfaceof the first electrode is uninsulated.

It is now disclosed for the first time a method of measuring penetrationin a root canal of a tooth of a patient. The presently disclosed methodincludes (a) inserting a first electrode into the root canal of a tooth,applying a second electrode to a body surface of the patient; (c)supplying a regulated current between the first and second electrodes,and (d) determining (e.g. measuring) an impedance parameter between thefirst and second electrodes, the impedance parameter indicative of adistance between a fixed point on the first electrode and an apicalposition of the tooth, wherein the determining includes determining acapacitance-determined impedance parameter when the fixed point is in anapical region of the root canal, and determining an impedance parameterwhose value is at least moderately governed by resistance when the fixedpoint is in a dental neck region of the root canal.

It is now disclosed for the first time a method of measuring penetrationin a root canal of a tooth of a patient. The presently disclosed methodincludes (a) inserting a first electrode into the root canal of thetooth, (b) applying a second electrode to a body surface of the patient,(c) supplying a regulated current between the first and secondelectrodes, and (d) determining (e.g. measuring) an impedance parameterbetween the first and second electrodes, and (e) deriving from thedetermined impedance parameter a multiple of a distance between a fixedpoint on the first electrode and the apical position of the tooth.

These and further embodiments will be apparent from the detaileddescription and examples that follow.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1-3 provide diagrams of exemplary systems for detecting an apicalposition according to some embodiments of the present invention.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

The present invention will now be described in terms of specific,example embodiments. It is to be understood that the invention is notlimited to the example embodiments disclosed. It should also beunderstood that not every feature of methods and devices for detectingan apical position are necessary to implement the invention as claimedin any particular one of the appended claims. Various elements andfeatures of devices are described to fully enable the invention. Itshould also be understood that throughout this disclosure, where aprocess or method is shown or described, the steps of the method may beperformed in any order or simultaneously, unless it is clear from thecontext that one step depends on another being performed first.

FIG. 1 provides a diagram of an exemplary device for detecting an apicalposition of a tooth 1 according to some embodiments of the presentinvention. Thus, as illustrated in FIG. 1, the tooth has a root canalwith a dental neck region 1 a and an apical section 1 b. A root canalelectrode 2 is inserted into the root canal 1 a, and the display unit 8of the device provides output indicative of a distance between a fixedpoint on the electrode 2 (e.g. the tip of the electrode 2 a) and a fixedpoint within the apical section 1 b. As shown in FIG. 1, a regulatedcurrent, for example an alternating current having a substantially fixedamplitude, flows between the root canal electrode and the externalelectrode 3, which contacts a surface of the patient's body.

In some embodiments, the position of the root canal electrode 2 may bedetermined by a processing unit 7 in accordance with electricalmeasurements for example, output generated by a voltmeter 5 between twolocations in the measurement circuit as will be explained below.

Experiments performed by the present inventors have shown that use of aregulated current source (e.g. a regulated alternating current source),and in particular, a current source having a substantially constantamplitude, is useful for producing stable measurements of the positionof the root canal electrode 2 within the root canal.

Not wishing to be bound by any particular theory, it is believed thatuse of a constant voltage source with un-regulated fluctuating current(e.g. current whose amplitude fluctuates as the root canal electrode isinserted deeper into the root canal, or raised in the canal) mayinfluence the electrical properties of the biological tissue associatedwith the root canal and the apex (for example, tissue in the canaland/or below the apex). Because the determined apical position dependson the measured electrical properties of the biological tissue, it isbelieved that use of a constant voltage source with un-regulatedfluctuating current can therefore, in certain situations, introduceinstabilities and inaccuracies in the assessed distance between the rootcanal electrode 2 and the apex (or apical constriction) of the tooth.Once more, not wishing to be bound by any particular theory, it is thusbelieved that, in contrast, regulated current sources, and in particulara current sources having a substantially constant amplitude, are usefulfor reducing these inaccuracies and instabilities certain clinicallyrelevant situations.

As used herein, production of “a regulated current” entails producing acurrent with a predefined current profile. Examples of producing a“regulated current” include producing a constant amplitude current and asubstantially constant amplitude current.

The terms “apical section” or “apical region” relate to the regionbetween the apical constriction (minor foramen) (or points less than 0.2mm above the apical constriction) and the apex (major foramen) of thetooth. It is noted the term “apical position” is intended in thebroadest sense, and includes any point in the apical region. In someembodiments, the “apical position” is specifically intended to mean theapex (major foramen) of the tooth.

The term “dental neck” region is the region of the root canal above theapical section, e.g. above the apical constriction, or above a pointbetween 0 and 0.2 mm above the apical constriction.

According to some embodiments, a “regulated current source 4A having asubstantially constant current amplitude” supplies, between the rootcanal electrode 2 and the external electrode 3, current whose amplitudeis constant within a tolerance of no more than 10%. According to someembodiments, the amplitude is constant within a tolerance of no morethan 5%. According to some embodiments, the amplitude is constant withina tolerance of no more than 1%.

As used herein, an “impedance related parameter” is a parameter that isa known function of an impedance. One example of an “impedance relatedparameter” is an impedance.

There is no limitation on the amplitude or amount of current which flowsbetween the root canal electrode and the external electrode. Inexemplary embodiments, between 1 microampere and 120 microamperes flowbetween the two electrodes. In some embodiments, between 5 microampereand 55 microamperes flow between the two electrodes. In one particularexample, between 8 and 12 microampere flow between the two electrodes.

According to exemplary embodiments of FIG. 1, the regulated orsubstantially constant amplitude current is supplied by a current supplydevice or measurement signal generator 4A adapted to send a current ithrough the optional wire terminal 11, the root canal electrode 2, andthe region between the tip 2A of the root canal electrode and theexternal electrode 3. In the example of FIG. 1, the wire terminal 11 isthe end of a flexible cable (e.g. about 5 ft long), and is connected tothe root canal electrode 2 with a spring clip 10. In the example of FIG.1, the external electrode 3 is an oral electrode connected to thegingival 6, though this is not a limitation of the present invention,and in various embodiments, the external electrode 3 may contact or be“applied to” any “body surface” of the patient. In one example ofapplying an electrode a “body surface” or contacting a “body surface,”the external electrode 3 contacts actual tissue of the patient outsideof the tooth. The term “body surface” includes, for example, any tissueof the patient, including tissue inside the patient's mouth and outsideof the patient's mouth, including, for soft tissue. In one example, the“body surface” is a patient's lip, or cheek. In one example, the “body,surface” is the patient's hands or feet. The term “applying anelectrode” to a body surface includes actually contacting the bodysurface, and/or contacting a conducting object or a partially conductingobject through which current flows to the body surface of the patient.

It is noted that constant amplitude current sources 4A are well known inthe art, and are either available off the shelf, or can be configured inany number of ways. FIG. 1B provides an exemplary configuration wherethe amplitude of a constant voltage source 4B is adjusted in accordancewith a reading from an internal voltmeter 10 on the circuit such thatthe current i remains substantially constant. Nevertheless, it isstressed that this is merely an illustrative example and is not intendedas limiting. Any constant amplitude current source using any mechanismfor maintaining a substantially amplitude current is within the scope ofthe present invention.

According to some embodiments, in one example, measurement output (e.g.output from a voltmeter 5) of an impedance parameter (e.g. a parameterthat is a function of the impedance at a given frequency) between theroot canal electrode 2 and the external electrode is determined. Themeasured impedance parameter (for example, derived by using thevoltmeter 5 to measure an instantaneous voltage amplitude between theroot canal electrode 2 and the external electrode 3) is correlated withthe depth of the root canal electrode tip in the root canal, allowingthe arrival of the tip at the root apex to be detected. Thus, in someembodiments, the device includes a processing unit 7 which is operativeto output a distance (or a multiple of a distance) between a fixed pointof the root canal electrode 2 (e.g. the tip of the electrode) and afixed point in the apical section 1B (e.g. the root apex, the locationof the apical constriction, or any other fixed point). In one example,the processing unit includes a look up table correlating theinstantaneous voltage amplitude measured by the voltmeter 5, with thedistance between a fixed point of the root canal electrode 2 (e.g. thetip of the electrode) and a fixed point in the apical section.

In the specific example depicted in FIG. 1, both the root canalelectrode 2 and the external electrodes 3 are “current supplyelectrodes”—e.g. electrodes which supply the regulated current from thecurrent supply device or measurement signal generator 4A through thebiological tissue between the electrodes. Furthermore, it is noted thatin the example of FIG. 1, the electric potential between the electrodesare measured, more example by electrode voltmeter 5, and thus theelectrodes (2 and 3) may also be considered “measurement electrodes.” Itis noted that the actual voltage between the measurement electrodes neednot be measured directly—in some embodiments, another parameter (e.g.electrical potential difference) indicative of the actual voltagebetween measurement electrode 2 and 3 (or the impedance between themeasurement electrode 2 and 3) is measured. Thus, according to theexample of FIG. 1, the current supply electrodes also function asmeasurement electrodes.

It is noted that optionally, a portion of the root canal, or theentirety of the root canal is filled with a liquid (e.g. saline, blood)and/or tissue (e.g. blood vessels, nerves, pulp) while the electrode 2is inserted into the root canal.

In some embodiments, the root canal electrode or probe 2 is a dentalfile or reamer inserted into the root canal. Nevertheless, this is not alimitation of the present invention, and any electrode or probeappropriately dimensioned for insertion into the root canal 2 isappropriate for the present invention.

The terms “dental file” and “reamers” relate to tools used for rootcanal treatment.

Not wishing to be bound by theory, it is noted that FIG. 2 provides anelectrical model of the root canal region. Thus, according to FIG. 2,the region between the root canal electrode 2 (e.g. the tip 2A of theroot canal electrode) and the external electrode 3 can be modeled as aresistor in parallel with the capacitor. The values of the resistanceand the capacitance vary as a function of the distance between the rootcanal electrode and the apex of the tooth. Thus, the present inventorsnote that while the tip of the root canal electrode is in the dentalneck or canal region 1A, the resistance component gradually decreases asthe root canal electrode 2 intrudes deeper into the root canal 1. In theapex region 1B, the value of the resistance component typically reachesa value of about 6.5 K Ohm.

Once more, not wishing to be bound by theory, it is further noted thatin contrast, the capacitive component, typically, is substantiallyconstant while the tip 2A of the root canal electrode is in the dentalneck or canal region 1B. The capacitive component typically increasesabruptly when the tip of the root canal electrode reaches the apexregion 1B.

According to these observations, the present inventors have noted thatthe resistive component of impedance is useful for determining thedistance between a fixed point on the root canal electrode 2 and a fixedpoint in the apex region 1B when the tip of the root canal electrode islocated in the dental neck region 1A. Furthermore, the capacitivecomponent of impedance is useful when the tip of the root canalelectrode is located in the apical region 1B.

In general, the relative weight of the resistive and capacitivecomponents of impedance is determined, in part, by the values of theresistance and capacitance between the two electrodes. Furthermore, therelative weight of the resistive and capacitive components of impedanceis also at least partially determined by the frequency of themeasurement signals generated by the power source of measurement signalgenerator 4. Thus, certain embodiments of the present invention aremotivated by the observation of the present inventors that a judiciouschoice of the measurement signal frequency (e.g. selection of a mediumfrequency) allows one to determine a distance between the fixed point onthe root canal electrode and the fixed point in the apex region 1B (e.g.apical constriction, or tooth apex) by determining the value of acapacitance-governed function when the root canal electrode is in theapical region 1B. Furthermore, this same medium frequency also allowsone determine a distance between the fixed point on the root canalelectrode and the fixed point in the apex region 1B (e.g. apicalconstriction, or tooth apex) by determining the value of a function atleast partially governed by resistance when the root canal electrode isin the dental neck region 1B. In some embodiments, “medium” frequencies,are between 50 KHZ and 300 KHZ. In some embodiments, “medium”frequencies, are between 50 KHZ and 200 KHZ. In some embodiments,“medium” frequencies, are between 50 KHZ and 250 KHZ.

As used herein, a “capacitance-governed function” is a function whosevalue is substantially independent of the value of resistance—e.g. afunction whose value does not fluctuate substantially (e.g. does notchange more than 5%, e.g. does not change more than 10%, e.g. does notchange more than 20%) with fluctuations in resistance between the twoelectrodes due to changing the position of the root canal electrode in acertain region of the root canal (for example, in the apical region).

As used herein, a “resistance-governed function” is a function whosevalue does not fluctuate substantially (e.g. does not change more than5%, e.g. does not change more than 10%, e.g. does not change more than20%) with variations in capacitance due to changing the position of theroot canal electrode. Typically, using a lower frequency (or directcurrent) will provide functions that do not fluctuate with variations inthe capacitance.

As used herein, a “function at least moderately governed by resistance”is a function whose value does fluctuate (e.g. at least 15%, e.g. atleast 30%) as values of the resistance changes (e.g. due to changing thepositions of the root canal electrode). Thus, a “resistance-governedfunction” is one special case of a “function at least moderatelygoverned by resistance.”

According to some embodiments of the present invention, the currentsupply device or measurement signal generator 4 is operative to generatea time varying current (e.g. an alternating current) having a frequencyof at least 50 KHZ. Furthermore, according to some embodiments of thepresent invention, the current supply device or measurement signalgenerator 4 is operative to generate a time varying current (e.g. analternating current) having a frequency of at most 300 KHZ, or at most200 KHZ.

It is noted that in the example provided, the device is a singlefrequency device, though this is not to be construed as a limitation ofthe present invention.

The following examples are brought for illustrative purposes only, andare not intended to limit the scope of the present invention.

Example 1 Experimental System

An evaluation system was built which provided a constant current of 10.8microamperes at a frequency of 65 KHz between two electrodes.

The sensed voltage between the electrodes was digitized by an 8-bitanalog digital converter (ADC), meaning that there were 255 possiblesignal levels. By appropriate scaling of the system (signal level andamplification, each level of the ADC represents 294 microvolt-RMS,between the electrodes). Since the current is 10.8 microamperes we get27.33 Ohms per level.

The impedance/distance curve was measured at about 10 microamperes.

The measured level was digitally displayed.

The following look-up table was used to correlate between the measuredimpedance between the two electrodes and the distance between the tip ofthe root canal electrode and the apex of the tooth (the first column isin mm, The second column is in Ohms. For example: at 0.2 mm theimpedance is 2.952 K Ohms.)

-   −0.1 2.405 E+3    0 2.651 E+3    0.1 2.815 E+3    0.2 2.952 E+3    0.3 3.088 E+3    0.4 3.252 E+3    0.5 3.416 E+3    0.75 3.799 E+3    1 4.072 E+3    1.5 4.373 E+3    2 4.591 E+3    2.5 4.783 E+3    3 4.947 E+3

Example 2 In Vitro Measurements

Extracted human teeth were inserted into a gum simulating mass(alginate). A dental file was pushed into the root canal of the measuredextracted tooth. Measurements were taken at several depths of the filewithin the root canal.

To be able to measure the depth of the file the following procedure wasused:

First, before putting the tooth into the alginate mass, the file waspushed into the extracted tooth until the file tip reached the apex.Then the distance between the file head and a reference point at thetopside of the tooth was measured, yielding the zero reference point.Next, the tooth was inserted into the alginate mass and the measuringprocedure began.

For each level, the voltage between the two electrodes was measured andtranslated into impedance.

The experiment was repeated several times per extracted tooth, and forseveral extracted teeth. Furthermore, as a control, the experiments wererepeated using other apex locators systems—namely a “Morita Root ZX” anda “Dentsply ProPex.”

Agreement was found between the measurements of the experimental systemand the other locator systems—e.g. “Morita Root ZX” and a “DentsplyProPex.”

Mechanical measurements of the distance between the apex and the tip ofthe root canal electrode were also made. The position measurement in mmwas done by using a calibrated digital micrometer down to 0.01 mmaccuracy/resolution. Agreement was found between the mechanicalmeasurements and those of the experimental system.

Example 3 Clinical Experiments

The clinical test prototype display of the experimental system showeddirectly the location as evaluated in the in-vitro tests.

We verified the reliability of the displayed values by using also theRoot ZX and comparing the reached working length (final position in thevicinity of the apical constriction) with radiographs. (X-Ray images).Agreement was found by results of the experimental system and theseother old systems.

Example 4 Exemplary System

Below is a specification of an exemplary systems in accordance with someembodiments of the present invention. Nothing in this example isintended as limiting. The entire example is intended only asillustrative. Furthermore, the skilled artisan will appreciate thecertain elements in this Exemplary system are option, and other elementscan be implemented in any number of ways.

FIG. 3 is a block diagram of the exemplary system.

A current source generates a sinusoidal signal of 65 KHz or and feeds itinto the tooth canal (“measured object”).

Due to the constant current source and the very large resistance of theparallel resistor R the voltage on the measured object is relative toits impedance. Therefore, voltages on the measured object correspond tothe impedances Z of the measured object.

Current Source

The signal current source provides 10.8 micro amps. At a frequency f=65KHz and is controlled by the processing unit.

The current is injected into the load every 1 msec for a period of about0.25 msec.

After an interruption of 0.75 msec, the frequency f is injected againand so forth periodically.

The peak value of the load current is protected to avoid exceeding 50μA.

No DC current is allowed through the electrodes.

Amplifier

The amplifier stages are high input impedance stages with high commonmode rejection as well as low frequency rejection.

Peak Detector

The peak detector is used for providing a measurement signal into theADC and is reset every 1 msec. The reset is synchronized with theeffective measurement signal.

ADC

The ADC converts the analog signal into a 256 level (8 bit) digitalsignal for evaluation by the processing unit.

The ADC is synchronized by the processing unit.

Controller/Processing Unit

Processing

The processing functions are:

-   -   1. Generation of the input modulation drive to the current        source.    -   2. Collecting ADC data and comparing to a preprogrammed        calibration table.    -   3. Calculating the distance between the file and the apex, using        a built in lookup table.    -   4. Converting the calculated location to input values for the        LCD.    -   5. Initiating buzzer signal according to the file location.

Control

The control functions are:

-   -   1. Management and synchronizing of the measurement process and        the signal flow (Peak detector, ADC).    -   2. Interface between the processing unit and the display and        controls.    -   3. Measuring the battery voltage and driving the battery        indication at the display.    -   4. Operating an audible signal.    -   5. Control the man machine interface (MMI).    -   6. Generate the internal system clock.    -   7. Generate and activate self test functions (if applicable).        Radio Communication

In a wireless operation version, the display input data is transmittedvia wireless radio link towards a compatible receiver which is connectedvia USB to the dental chair integrated monitor. Specially installedsoftware will provide a replica of the LCD on the monitor. The graphicappearance on the external monitor is designed separately.

External Interface

Connectors

-   -   1. Electrodes' connector: Standard earpiece connector

Controls

-   -   1. On/off—Pushbutton, 1 sec pressing for on or off activation.        The unit will automatically turn off after 20 minutes.    -   2. Buzzer volume control.    -   3. Display illumination control.    -   4. Apical constriction indication signal level.

Display

-   -   1. Indications:        -   a. The length display is between −0.3 mm and +3.0 mm. The            scale is logarithmic for the values 0.0 to 3.0 mm, and            linear for the values 0.0 to −0.3 mm        -   b. Continuous beep in the range between Apical Constriction            and Apex.        -   c. On/Off beep at APEX location: 0.0 mm.        -   d. At the value of the Apical Constriction (nominally at            0.5 mm) a special indication is seen on the display. This            indication is pre-settable by the user in the range of 0.5            mm to 1.0 mm.    -   2. Battery voltage, audible signal at low battery.    -   3. On/Off indication of switch (display indications are        observable).

Measuring Probes

The measuring probes consist of a two wire flexible cable 5 ft long.

One end is terminated with an earphone connector. The other end is splitinto two wires of 1 ft length.

One wire is terminated with a hook shaped electrode and the other with aspring clip electrode to be connected to the file.

Both types of electrode are detachable and replaceable.

Both types of electrode are autoclavable.

In the description and claims of the present application, each of theverbs, “comprise” “include” and “have”, and conjugates thereof, are usedto indicate that the object or objects of the verb are not necessarily acomplete listing of members, components, elements or parts of thesubject or subjects of the verb.

The present invention has been described using detailed descriptions ofembodiments thereof that are provided by way of example and are notintended to limit the scope of the invention. The described embodimentscomprise different features, not all of which are required in allembodiments of the invention. Some embodiments of the present inventionutilize only some of the features or possible combinations of thefeatures. Variations of embodiments of the present invention that aredescribed and embodiments of the present invention comprising differentcombinations of features noted in the described embodiments will occurto persons of the art. The scope of the invention is limited only by thefollowing claims.

1. Apparatus for detecting an apical position depending on the change inthe impedance between a first current supply electrode inserted into theroot canal of a tooth of a patient and a second current supply electrodecontacting a body surface of the patient, the apparatus comprising: a) adetection apparatus including a measurement signal generator adapted toproduce a regulated current between the first and second current supplyelectrodes, said detection apparatus adapted to sense animpedance-related parameter between the first and second current supplyelectrodes; and b) a processing unit for deriving from said sensedparameter a multiple of a distance between a fixed point on the firstcurrent supply electrode and the apical position of the tooth, whereinsaid regulated current has an amplitude that is substantiallyindependent of a distance between said fixed point and the apicalposition.
 2. The apparatus of claim 1 wherein said regulated current hasa substantially constant current amplitude.
 3. The apparatus of claim 1wherein said regulated current is a time varying current having afrequency of at least about 50 KHz.
 4. The apparatus of claim 3 whereinsaid regulated current is a time varying current having a frequency ofat least about 50 KHz and at most about 200 KHz.
 5. The apparatus ofclaim 1 wherein said processing unit determines a capacitance-governedfunction when the first electrode is in the apical region, and saidprocessing unit determines a function at least moderately governed byresistance when the electrode is in a dental neck region.
 6. Theapparatus of claim 1 wherein said processing unit determines acapacitance-governed function when the first electrode is in the apicalregion, and said processing unit determines a function moderatelygoverned by resistance when the electrode is in a dental neck region. 7.The apparatus of claim 1 wherein said detection apparatus is adapted tosense the impedance-related parameter and said processing unit isconfigured to sense the distance multiple without relying on measurementsignals at multiple frequencies.
 8. The apparatus of claim 1 whereinsaid detection apparatus is adapted to produce the regulated currentbetween the electrodes at a single frequency of at least about 50 KHz.9. A device comprising: a) a dental file electrode insertable into theroot canal of a tooth of a patient; b) an external electrode adapted tocontact a body surface of the patient; and c) a detection apparatusincluding a measurement signal generator adapted to produce a regulatedcurrent between said dental file and external electrode, said detectionapparatus adapted to sense an impedance related parameter to generate anoutput signal indicative of a distance between a fixed point on saiddental file electrode and the apical position of the tooth, wherein saidregulated current has an amplitude that is substantially independent ofa distance between said fixed point and the apical position.
 10. Thedevice of claim 9 wherein said regulated current is a substantiallyconstant amplitude current.
 11. The apparatus of claim 9 wherein saiddetection apparatus is adapted to sense the distance-indicativeimpedance-related parameter without relying on measurement signals atmultiple frequencies.
 12. The apparatus of claim 9 wherein saiddetection apparatus is adapted to produce the regulated current betweenthe electrodes at a single frequency of at least about 50 KHz.
 13. Thedevice of claim 9 further comprising: d) a processing unit for derivingfrom said output signal a multiple of a distance between said fixedpoint on said first electrode and said apical position of the tooth. 14.The device of claim 13 wherein said processing unit determines acapacitance-governed function when the first electrode is in the apicalregion, and said processing unit determines a function moderatelygoverned by resistance when the electrode is in a dental neck region.15. A method of measuring penetration in a root canal of a tooth of apatient comprising: a) inserting a first electrode into the root canalof a tooth; b) applying a second electrode to a body surface of thepatient; c) supplying a regulated current between said first and secondelectrodes; and d) determining an impedance parameter between said firstand second electrodes, said impedance parameter indicative of a distancebetween a fixed point on said first electrode and an apical position ofsaid tooth, wherein said first electrode is inserted to a plurality ofdepths within said root canal, and an amplitude of said regulatedcurrent is substantially independent of said distance between said fixedpoint and said apical position.
 16. The method of claim 15 wherein saiddetermining of said distance-indicative parameter is carried out withoutrelying on measurement signals at multiple frequencies.
 17. The methodof claim 15 wherein electrical current at only a single frequency of atleast about 50 KHZ is supplied between said first and second electrodes.18. The method of claim 15 wherein said second electrode is applied tosaid position within the oral cavity of the patient.
 19. The method ofclaim 15 wherein said second electrode is applied to said positionoutside of the oral cavity of the patient.
 20. The method of claim 15wherein said regulated current is a time varying current, and afrequency of said time varying current is at most about 250 KHZ.
 21. Themethod of claim 15 wherein said regulated current is a time varyingcurrent, and a frequency of said time varying current is at least about50 KHZ.
 22. The method of claim 15 wherein said determining includesdetermining a capacitance-determined impedance parameter when said fixedpoint is in an apical region of said root canal, and determining animpedance parameter whose value is at least moderately governed byresistance when said fixed point is in a dental neck region of said rootcanal.
 23. The method of claim 15 further comprising: c) deriving fromsaid determined impedance parameter a multiple of a distance betweensaid fixed point on said first electrode and said apical position of thetooth.
 24. The method of claim 23 wherein said deriving of said multipleof said distance includes deriving a capacitance-governed function whensaid fixed point is in an apical region of said root canal, and derivinga function at least moderately governed by resistance when said fixedpoint is in a dental neck region of said root canal.
 25. A method ofmeasuring penetration in a root canal of a tooth of a patientcomprising: a) inserting a first electrode into the root canal of atooth; b) applying a second electrode to a body surface of the patient;c) supplying a regulated current between said first and secondelectrodes; and d) determining an impedance parameter between said firstand second electrodes, said impedance parameter indicative of a distancebetween a fixed point on said first electrode and an apical position ofsaid tooth, wherein said determining includes determining acapacitance-determined impedance parameter when said fixed point is inan apical region of said root canal, and determining an impedanceparameter whose value is at least moderately governed by resistance whensaid fixed point is in a dental neck region of said root canal.
 26. Themethod of claim 25 wherein said determining of said distance-indicativeparameter is carried out without relying on measurement signals atmultiple frequencies.